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Mittal RK. Motor Function of the Pharynx, Esophagus, and its Sphincters. San Rafael (CA): Morgan & Claypool Life Sciences; 2011.

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Motor Function of the Pharynx, Esophagus, and its Sphincters.

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Deglutitive Inhibition and Muscle Refractoriness

Intraluminal pressure recordings show that each swallow induces a peristaltic contraction that traverses the entire length of the esophagus. It takes 6–10 seconds for the contraction wave to arrive at the distal esophageal end. However, if the subject swallows for the second time, before the contraction from the first swallow has a chance to complete its journey through the esophagus, i.e., within 4–6 seconds, the second swallow inhibits the contraction that would have been produced by the first swallow. Multiple swallows in rapid succession, i.e., at closely spaced intervals elicit only one peristaltic contraction that follows the last swallow [107109] (Figure 12). In other words, esophagus remains silent during the period of rapid swallows, and LES remains relaxed. Above phenomenon, known as deglutitive inhibition, initially described by Dotty, allows fast drinking of fluids and beer guzzling [1]. During rapid swallows, larynx remains elevated and upper esophageal sphincter remains open, pharynx may or may not contract, esophageal and LES remain relaxed [14]. Esophagus becomes a simple conduit for the transfer of fluid pumped by the oropharynx into the stomach. If person swallows for the second time soon (within 10 seconds) after the completion of first peristaltic contraction, amplitude of contraction related to the second swallow is lower than the first swallow, a phenomenon related to the refractoriness of esophageal muscle [108,109]. As discussed later, central (brain stem) as well as peripheral mechanisms (within the smooth muscle esophagus) exist for the deglutitive inhibition. Initial inhibition and refractoriness form the basis for the clinical practice of spacing swallows at least 30 seconds apart during esophageal motility studies.

Motor events associated with the retrograde transport, i.e., belching, gastroesophageal reflux, regurgitation, rumination, and vomiting, are distinct from primary and secondary peristalsis. These events begin with spontaneous relaxation of the LES or transient LES relaxation, described in exquisite detail in the context of gastroesophageal reflux events. Transient LES relaxation was discovered in the context of gastroesophageal reflux, which is thought to be a “pathological event.” Even though there is a major mechanism of reflux in patients with reflux disease, transient LES relaxation and physiological reflux occur in normal healthy subjects fairly frequently. Transient LES relaxation is also the key motor event during rumination and vomiting (physiological events). Transient LES relaxation is unrelated to swallowing and is accompanied by simultaneous relaxation of the LES and crural diaphragm [110] along with the inhibition or contraction in the body of the esophagus. The hallmark of transient LES relaxation is that it is significantly longer (>10 seconds) than the swallow-induced LES relaxation (<10 seconds) [111] (Figure 14). Esophagus remains relatively quiescent during transient LES relaxation. However, a study that used a small distended balloon in the distal esophagus to record muscle activity found contraction of the distal esophagus [112]. During rumination and vomiting, retrograde contraction or reverse peristalsis of the esophagus has been observed using radiological studies [113]; however, pressure recordings generally do not show it. Contraction of the abdominal wall and costal diaphragm, by reducing size of abdomen cavity, increases intragastric pressure to provide propulsion force for the gastric contents to move into the esophagus and pharynx during vomiting and rumination. Generally, there is no increase in the gastric pressure in association with gastroesophageal reflux. Refluxed contents into the esophagus, whether they make it to the pharynx, depend on whether UES contracts or relaxes. It appears that the rapidity of esophageal pressure increase caused by reflux is the major determinant for UES relaxation, e.g., air reflux into the esophagus especially in the upright position that causes rapid increase in intraesophageal pressure is associated with UES relaxation [43]. On the other hand, liquid reflux, especially in the supine position is associated with slower increase in the esophageal pressure and UES contraction [44].

FIGURE 14. Swallow-induced and transient relaxation of the LES.

FIGURE 14

Swallow-induced and transient relaxation of the LES. Swallow-induced LES relaxation is a brief 6–8 seconds and follows swallow-induced pharyngeal contraction. On the other hand, transient LES relaxation is not preceded by a swallow and lasts for (more...)

Copyright © 2011 by Morgan & Claypool Life Sciences.
Bookshelf ID: NBK54285
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